When a road vehicle is equipped with a vehicle monitoring device, which is capable of outputting and/or displaying vehicle operating parameters, such as fuel economy, exhaust emissions, or engine load, the device needs to be calibrated to reflect the specific characteristics of the vehicle to which it is attached over its operating ranges, both under load and in various climatic conditions. The device may additionally need to be recalibrated on an on-going basis to reflect its load or the operating conditions or characteristics of the vehicle.
The vehicle monitoring device may be programmed to be able to output the exhaust tailpipe emissions of the vehicle, for example to ensure compliance with regulations. It will also need to be calibrated for these outputs to be reliable.
In principle this could be achieved by providing a large number of data inputs to the device or by laboratory testing of each vehicle but these processes would be impracticable and expensive.